1. Field of the Invention
The present invention relates to systems and methods wherein a pump is utilized to draw a vacuum within a work processing chamber. Particularly, the present invention relates to the use of a vacuum responsive throttle valve for regulating the pumpdown phase of a process with the system.
2. Description of Related Art
In numerous industries, processes must be carried out within a vacuum. For example, in the polymer, pharmaceutical, munitions, and pigment industries, powders are dried in vacuum, as are particular construction materials. In such cases, if a vacuum is drawn too rapidly, associated turbulence can result along with a so-called "puffing" of the particulate matter (i.e., a sudden upheaval of the material due to the initial surge in the system). In turn, the dislodged particles can cause clogging of the filter that is normally provided between the pump and the vacuum processing chamber. Furthermore, in the case of very fine powders, some of the powder can even pass through the filter and reach the pump, thereby potentially damaging the pump itself.
Likewise, problems can occur if initial pumpdown occurs to rapidly during degassing of liquids, since splattering can result, and analogous problems exist in pulp and paper processing, as well as in the performance of pressure-dependent chemical reactions. Likewise, in silicon wafer processing as occurs in the semiconductor industry, work surface contamination from airborne particulates is a significant problem, which is, in part, affected by system turbulence which results in the contamination or aggregation of particulate in a system component.
Still further, because liquid ring pumps are less of an environmental contaminant and are more energy efficient than two-stage steam ejectors, companies having two-stage steam ejectors can benefit from replacing them with a liquid ring pump. However, liquid ring pumps have a much more rapid pumpingdown capability than steam ejectors, so that, in many cases, there is a need to throttle-down the liquid ring pump for it to be usable, because of a need to reduce turbulence and/or increase the pumpdown time.
It would be possible to achieve a slowing-down of the pumpdown process by providing the pump with a programmable logic controller. However, such are costly and not readily adaptable to all existing vacuum pump systems.
Vacuum responsive, spring-biased, diaphragm-type valves controllers are known for use in shifting the position of a butterfly valve in response to changes in the vacuum pressure to which it is exposed. For example, Troyer U.S. Pat. No. 4,299,373; Sheppard U.S. Pat. No. 4,073,465; and Stratynski U.S. Pat. No. 3,929,314, all show such controllers used in conjunction with butterfly-type fluid flow control valves. However, in each of these patents, the vacuum used for controlling the position of the butterfly valve plate is drawn from the vacuum manifold of an engine for regulating the flow of a liquid through the cooling system of the engine as a function of engine operating conditions, as opposed to responding to the pressure of the controlled flow. Furthermore, in all of these butterfly-type throttle valves, no flow is permitted across the butterfly valve plate when the valve plate is in its closed position.
Additionally, the use of the pressure of a controlled fluid for controlling the position of a valve in a supply conduit for the fluid is also known. Typical of such arrangements are Williamson U.S. Pat, No. 2,445,163; McRae U.S. Pat. No. 2,744,719; and Goodman, et al. U.S. Pat. No. 4,316,597. However, none of these devices are designed so as to be capable of being vacuum responsive, and thus, none of these systems deal with any of the various factors of significance in vacuum processing systems and methods. In fact, as opposed to providing a slow, automatic opening of a throttle valve, the Williamson patent is manually controlled by a hand lever, and the McRae patent is designed to produce a quick opening and closing, as opposed to a deliberately slow one.
Thus, there is a need for a simple and inexpensive flow control system and process for obtaining vacuum processing under conditions where a slow pumping-down of the system is achieved, and especially, in a manner that can be adapted to virtually any system, irrespective of the type of vacuum pump involved.